SHORT VIDEO INTRODUCTION

Program and Programmer

• Program: set of instructions that a computer follows to perform a task
  • Commonly referred to as Software
• Programmer: person who can design, create, and test computer programs
  • Also known as software developer

Central processing unit

• Central processing unit (CPU): the part of the computer that actually runs programs
  • Most important component
  • Without it, cannot run software
  • Used to be a huge device
• Microprocessors: CPUs located on small chips

Main memory

• Main memory: where computer stores a program while program is running, and data used by the program
• Known as Random Access Memory or RAM
  • CPU is able to quickly access data in RAM
  • Volatile memory used for temporary storage while program is running
  • Contents are erased when computer is off

Secondary storage devices

• Secondary storage: can hold data for long periods of time
  • Programs normally stored here and loaded to main memory when needed
• Types of secondary memory
  • Disk drive: magnetically encodes data onto a spinning circular disk
  • Solid state drive: faster than disk drive, no moving parts, stores data in solid state memory
  • Flash memory: portable, no physical disk

Input devices

• Input: data the computer collects from people and other devices
• Input device: component that collects the data
  • Examples: keyboard, mouse, touchscreen, scanner,camera
  • Disk drives can be considered input devices because they load programs into the main memory

Output devices

• Output: data produced by the computer for other people or devices
  • Can be text, image, audio, or bit stream
• Output device: formats and presents output
  • Examples: video display, printer -Disk drives and USB drives can be considered output devices because data is sent to them to be saved

Software

• Everything the computer does is controlled by software
  • General categories:
    • Application software
    • System software
• Application software: programs that make computer useful for every day tasks
• Examples: word processing, email, games, and Web browsers

• System software: programs that control and manage basic operations of a computer
  • Operating system: controls operations of hardware components
  • Utility Program: performs specific task to enhance computer operation or safeguard data
  • Software development tools: used to create, modify, and test software programs

Principal

• All data in a computer is stored in sequences of 0s and 1s
• Byte: just enough memory to store letter or small number
  • Divided into eight bits
  • Bit: electrical component that can hold positive or negative charge, like on/off switch
  • The on/off pattern of bits in a byte represents data stored in the byte

Storing Characters

• Data stored in computer must be stored as binary number
• Characters are converted to numeric code, numeric code stored in memory
  • Most important coding scheme is ASCII
    • ASCII is limited: defines codes for only 128 characters
  • Unicode coding scheme becoming standard
    • Compatible with ASCII
    • Can represent characters for other languages

Advanced Number Storage

• To store negative numbers and real numbers, computers use binary numbering and encoding schemes
  • Negative numbers encoded using two’s complement
  • Real numbers encoded using floating-point notation

Other Type of Data

• Digital: describes any device that stores data as binary numbers
• Digital images are composed of pixels
  • To store images, each pixel is converted to a binary number representing the pixel’s color
• Digital music is composed of sections called samples
  • To store music, each sample is converted to a binary number

CPU

• CPU designed to perform simple operations on pieces of data
  • Examples: reading data, adding, subtracting, multiplying, and dividing numbers
• Understands instructions written in machine language and included in its instruction set
  • Each brand of CPU has its own instruction set
• To carry out meaningful calculation, CPU must perform many operations

• Program must be copied from secondary memory to RAM each time CPU executes it
• CPU executes program in cycle:
  • Fetch: read the next instruction from memory into CPU
  • Decode: CPU decodes fetched instruction to determine which operation to perform
  • Execute: perform the operation

From Machine Language to Assembly Language

• Assembler: translates assembly language to machine language for execution by CPU
• Assembly language: uses short words (mnemonics) for instructions instead of binary numbers
  • Impractical for people to write in machine language
  • Easier for programmers to work with

High-Level Languages

• Low-level language: close in nature to machine language
  • Example: assembly language
• High-Level language: allows simple creation of powerful and complex programs
  • No need to know how CPU works or write large number of instructions
  • More intuitive to understand

Keywords, Operators, and Syntax: an Overview

• Keywords: predefined words used to write program in high-level language
• Each keyword has specific meaning
• Operators: perform operations on data
• Example: math operators to perform arithmetic
• Syntax: set of rules to be followed when writing program
• Statement: individual instruction used in high-level language

• Interpreter: translates and executes instructions in high-level language program
  • Used by Python language
  • Interprets one instruction at a time
  • No separate machine language program

• Source code: statements written by programmer
• Syntax error: prevents code from being translated

Interactive Mode

• When you start Python in interactive mode, you will see a prompt
  • Indicates the interpreter is waiting for a Python statement to be typed
  • Prompt reappears after previous statement is executed
  • Error message displayed If you incorrectly type a statement
• Good way to learn new parts of Python

Writing Python Programs and Running Them in Script Mode

• Statements entered in interactive mode are not saved as a program
• To have a program use script mode
  • Save a set of Python statements in a file
  • The filename should have the .pyextension
  • To run the file, or script, type python filename at the operating system command line

The IDLE Programming Environment

• IDLE (Integrated Development Program): single program that provides tools to write, execute and test a program
• Automatically installed when Python language is installed
• Runs in interactive mode
• Has built-in text editor with features designed to help write Python programs